Powder metallurgy forging

ABSTRACT

Steel powder forged at a temperature at which the steel is characterized by a microstructure containing specified percentages of ferrite and austenite contributes to low flow stress and other indicated advantages.

United States Patent 1191 Church *Aug. 5, l975 [54] POWDER METALLURGYFORGING 2.942.334 6/1960 Blue 75/,5 BA

2.967.794 l/l9fil Coxe 75/.5 BA [75] memo Church 3.702.791 11/1972Freche ct a|....... 29/4205 x 3.720.512 3/1973 Yamaguchi el 111....75/221 [-73] Assigneez The lnternafional Nickel p y 3.787.205 l/l974Church 29/4205 X -i New York NY. FOREIGN PATENTS 0R APPLICATIONS lNotice: The portion of the term of this 1.281.734 7/1972 United Kingdom9 fizfg jg gg gfg f OTHER PUBLICATIONS Shape. E. et al.. MicroduplexProcessing of Low [22] 1974 Alloy Steels." Journal of Metals, Jan. 1972.pp. [2]] Appl. No.: 448,823 23-29.

Related US. Application Data w [62] Division of Ser. No. 238,238. March27, 1972. Pat.

No 3.837845- Ass/stun! ExaminerD. C. Reiley, lll

Attorney, Agent. or Firm-Raymond J. Kenny; Ewan [52] us. (:1. 29/4205;29/420; 29/010. 31 Macouee" [51] Int. Cl 822i 3/24 [58] Field of Search29/420, 420.5, DIG. 31; [57] ABSTRACT 7 75/5 1, Steel powder forged at atemperature at which the steel is characterized by a microstructurecontaining specified percentages of ferrite and austenite contrib- [56]UN]TE ;s E S utes to low flow stress and other indicated advantages.2.809.89! 10/1957 Ennor et al. 75/220 1 Drawing 8" ml I'll I1 I "II "IIIIl'll IF- IJ lI-lI-III. (Bill I. i l

ll. 1' III Ylllllll' III I'll-P PATENTEU RUB 5 I975 TEMPERATURE (F)-POWDER METALLURGY FORGING This is a division, of application Ser. No.238,238, filed Mar. 27, 1972, now U.S. Pat. No. 3,837,845.

The subject invention is addressed in the main to powder metallurgyalloy steel forging.

As the metallurgist is aware, powder metallurgy has for some time playeda prominent role in the production of a number of useful structuralcomponents. This has been particularly evident in respect of productsnot readily responsive to the more conventional meltingcasting-workingtype processing, notably the production of intricately shaped products,certain refractory metals and alloys, various dispersion hardenedmaterials, etc.

The virtues of powder metallurgy notwithstanding, the customarycompacting and sintering techniques nonetheless gave rise to anattendant porosity problem, i.e., a problem in which products as finallyprocessed are characterized by voids which in turn detract from variousmechanical and/or physical properties, e.g., yield strength, impactenergy, etc. This difficulty has quite naturally served to restrict thescope and application of powder technologyv To be sure, a number oftechniques have been devised to minimize this porosity drawback. Mentionmight be made of repressing and/or infiltration as well as conductingboth the compacting and sintering operations at high temperature. Suchprocedures, however, do introduce added cost and/or do not lendthemselves to mass production techniques.

In recent years powder metalurgy (P/M) forging, an historically old andnear forgotten art, has received considerable attention since it offersan economically attractive panacea for virtually eliminating porositywhile being amenable to automation. in large part, at least to date,powder forging investigations in the steel area seemingly have beenconfined to relatively conventional wrought alloy compositions and thosepreviously used in the sintering industry, perhaps because theirproperties were of a known quantity and thus offered some basis forcomparison. Illustrative of this are the higher carbon AlSl 4600 typesteels.

Be that as it may, the present invention is particularly concerned withnew steels which by virtue of their chemistry enhance the carrying forthof the WM forging process and/or which by virtue of the forging processare rendered particularly useful. It is to be understood, however, thatthe instant invention does not exclude steels the composition per se ofwhich might heretofore have been known.

It has now been discovered that improvements involving alloy steelpowder forging can be brought about provided the forging operation iscontrolled such that it is conducted at a temperature at which the steelis characterized by a special structure as herein de scribed.

Generally speaking, the present invention contemplates the forging ofpowder alloy steels characterized at the temperature of forging by amicrostructure in which the alloy steel powders are comprisedessentially of the ferrite and austenite phases, these phases mutuallycoacting such that grain growth is retarded during recrystallization.Advantageously, at the forging temperature both the ferrite andaustenite are present in a volume percentage of at least about percentwith their respective grains not exceeding an average ASTM grain size ofabout 10, the grain size most advantageously being not greater thanabout ASTM 12.

In accordance herewith, upon bringing the steels to the desiredmicrostructural condition and forging at a temperature which does notdeleteriously disrupt this condition, it is deemed that any one or moreof a number of benefits follow, e.g., improved die filling, lowerforging loads for a given configuration, less oxidation, the likelihoodof decreased die wear, breakage or distortion, lower cost, etc.

For example, with respect to the low alloy steels herein illustrated, itwas found that such steels when in the proper ferritic austeniticcondition manifest a markedly lower flow stress (less resistance toflow) than might otherwise be the case. In conjunction there with it wasfurther determined that a significantly lower forging temperature couldbe used as opposed to the necessity of using one much higher as is theprevailing conventional practice. By reason of such (and other)characteristics, it is considered that, for example, longer die lifeshould obtain and, thus, less downtime as well. And as is known, giventhe complexities of die configurations coupled with the productionproblems associated therewith, die life is an important economiccomponent in the equation determinative of whether the manufacture of agiven product is likely to be competitive.

The following novel alloy steel compositions are considered particularlybeneficial since in addition to manifesting low flow strengths at theprerequisite forging temperature they afford high strength at roomtemperature: about 0.05 to 0. l5 percent carbon; about 0.8 to 25 percentsilicon; up to about 2 percent manganese; about 0.5 to 4 percent nickel;about 0.2 to 2 percent molybdenum; up to about 2 percent, e.g., 0.8 to1.75 percent, copper; up to 0.2 percent, e.g., 0.02 to 0.12 percent,columbium', up to 0.15 percent or 0.25 percent, e.g., from 0.01 percentor 0.03 to 0.12 percent, oxygen, the balance being essentially iron andimpurities. Such compositions can be compacted and forged to virtuallydensity at about l400l500F., e.g., 1450F., in contrast to temperatureson the order of 16501 800F. commonly employed in conjunction withcurrent low alloy steel P/M forging practice.

In terms of the ferrite and austenite phases, while the volumepercentage of each may be as low as 4 or 5 per cent, in striving for anoverall good combination of physical and/or mechanical properties,including flow strength, room temperature strength, etc., at least 10percent, and most beneficially about 20 percent or more, of each shouldbe present at the forging temperature. A microstructure at that pointcontaining, say, I to 2 percent ferrite, balance austenite would berather unsuitable since, inter alia, it would exhibit a higher flowstrength and there would be insufficient ferrite to prevent undesirablegrain growth in the austenite. In this connection and as indicatedabove, the grains of these phases prior to forging and at thetemperature of forging should be at least about ASTM grain size 10 onaverage. The grains can be larger, e.g., ASTM 8, but generally at theexpense of some mechanical or physi cal property. ASTM 14 or smaller isconsidered beneficial particularly in respect of various properties.Grain size applies to the forged products as well.

Concerning the powder particles, while elemental powders might beblended and sintered to the desired composition, it is deemed muchpreferable to use prealloyed powder. As will be appreciated by theartisan, this can, for example, be accomplished through atomization inwhich a liquid melt of desired composition is formed and directlyconverted to powder by using air, steam, inert gas, vacuum or water tobring about atomization. Water atomization, with or without an inertgaseous stream, is considered appropriate since it is commonly employedand is relatively inexpensive. Prealloying and atomization provide forsmall particle size and grain size. Moreover, it is preferred that theparticles as alloyed be of irregular shape as opposed to, say,spherical. This enhances particle interlocking.

The alloy powders should not exceed about 500 microns (including oxidefilm), preferably being less than 275 microns, an advantageous powdermix being one containing not more than 25 percent of powder less than 40microns in size, the remainder being up to 225 or 275 microns. Thesurface of the powder particles is substantially, if not completely,comprised of an oxide film but this is beneficial in accordanceherewith. This inhibits grain growth within each particle as well asinhibiting growth across interparticle boundaries. Though up to possiblyl percent oxygen can be present in the steels, high oxygen impairstoughness, detracts from compacting and sintering prior to forging andre' tards interparticle welding during forging. The oxygen level shouldnot exceed about 0.25 percent and the oxide film thickness should beless than about 5 or microns.

The prealloyed powder particles are thereafter compacted to a preform,the shape of which will often, though not necessarily, depend on theshape of the final product. Thereupon, the prealloyed preform is heatedto obtain the desired ferritic-austenitic mierostructure whereupon it isforged to shape and full or nearly full density. As is often done inpractice, an appropriate lubricant can be added to the prealloy powderbefore pressing to the preform. Also, the prefrom can be heated(sintered) prior to forging in accordance with usual practice.Subsequently, the product may, if desired and depending on composition,be further processed, e.g., machined or aged in the case of age hardenable materials or normalized, carburized, nitrided,

etc.

In order to give those skilled in the art a better appreciation of theadvantages of the invention, the following data are given.

Several steel compositions were prepared by atomizing prealloyed melts,the chemistry of which are given in Table I. The atomized powders weremade from air induction melted heats using a magnesia crucible. Electrolytic iron and nickel were first charged and melted and thenmolybdenum pellets were added. The melts were heated to 2850F. and pigiron (to add carbon for carbon boil) added. Following a 5 minute boilhalf the silicon (ferro form) was added together with pig iron and, ifany, ferromanganese, ferrocolumbium and copper, the remainder of thesilicon being added. The melts were tapped at 2850F. atomized with argonat 400 psi under an argon atmosphere and the prealloyed powders werethen screened into various mesh sizes. Argon was used since wateratomization facilities were unavailable.

contained 0.12X Ti and 0.002% B and 0.65% Mn n.u. not added n.d. notdetermined While all the alloys above were tested, a few specificexamples will be given as illustrative.

EXAMPLE I This example is illustrative of a low alloy steel combininghigh yield strength and good ductility, it being a specific objective ofthe invention to provide a steel with a yield strength of at least90,000 psi together with a tensile ductility of about 10 percent ormore.

Using 40 to +100 mesh particles, Alloy l was sealed in a mild steelmetal can (3 inches inside diameter, 6 inches long, A inch thick walls)and rolled (starting temperature of l650F. to fully dense (no obviousvoids) inch thick plate, the mill speed being about 40 ft./min. The canwas machined off and specimens for room temperature and hot tensiletests were cut from the plates, aged about 4 hrs. at 1000F. and aircooled. The following tensile properties were obtained at roomtemperature: yield strength, 125,100 psi; ultimate tensile strength,125,100 psi; elongation (in 0.55 inch), l 1.5 percent; reduction inarea, 30.5 percent; R. hardness, 27.2.

To simulate expected powder forging behavior, the steel was tensiletested at various true strain rates. Flow strength was determined at thevarious strain rates at 1450F The data include a similarly processed andcur rently used powder forging steel (Ailoy A) nominally containingabout 0.5 percent C., .35 percent Mn., 0.01 percent P, 0.02 percent S,0.45 percent Ni and 0.55 percent Mo.

True Stress True Strain (psi) in/in/min Alloy 1 Alloy A It will beobserved that at the temperature of 1450F.

Alloy l of the invention had a markedly lower flow strength at all threestrain rates. This should contribute to enhanced die filling and/orresult in less die wear and distortion in hot forging. it should beemphasized this was achieved notwithstanding that the yield strengththereof exceeded that of Alloy A by about 36,000 psi, the elongation ofthe latter being only 7.5 percent. Actually, Alloy 1 had a lower flowstress at 1450F. than Alloy A at l650F. Alloy 1 upon being canhot-rolled, heated at 1450F. for V2 hour and cooled (approximab ing anair cool) had a fine grained microstructure which by visual observationconsisted of about 10 to 20 percent ferrite, less than 2 percentaustenite (as determined by X-ray), the balance being the decompositionproducts of austenite. Grain size was less than ASTM EXAMPLE 11 TrueStress True Strain (psi) in/in/min. Alloy 2 Alloy A 5,740 [4,200 0.006IU,57O H1330 0.064 H4290 26,050 0.528

Alloy 2, tested as in Example I, had a microstructure of about 25 35percent ferrite the remainder being similar to Alloy 1. Grain size wasabout ASTM 12-14.

EXAMPLE III Alloy 3 is representative of a steel useful forcarburization purposes subsequent to forging. After applying a heattreatment cycle quite similar to that used in carburizing (but withoutthe carbon), the heat treatment consisting of 40 min. at 1700F., oilquenching, plus 3 hrs. at 300F. and air cooling, the followingproperties were obtained: yield strength (0.2 percent offset), [40,300psi; ultimate tensile strength 188,600 psi; elongation (in 0.55 inch),l4.5 percent; and a reduction in area of 33 percent. These propertiesare indicative of those to be expected in the core of a carburized part.Carburizing at l700F. at 0.95 percent carbon potential, then oilquenching and tempering at 300F. for 3 hours resulted in lower ductilityin another specimen of Alloy 3. About 15 25 percent ferrite,approximately 2 percent austenite with the balance being thedecomposition products of austenite, constituted the microstructure astested in Example I.

FIG. 1 graphically depicts the true stress at a true strain rate ofabout 0.6 in/in/min at a temperature of l450F. for Alloys 1-9. Curve Xis specific to Alloy l and spans the 1400F. I500"F. temperature range.Curve Y is specific to Alloy A. It can be seen that I400F. stress forAlloy l is comparable to that of Alloy A at I600F. despite the fact thatthe latter had the benefit of the much higher temperature.

Among other attributes of the above steels in comparison with the highcarbon AISI 4600 steels and other proposed high carbon steels, might belisted the follow ing: (a) they do not require heating to the austeniterange, e.g., l700F. and above, followed by rapid cooling and tempering,a treatment which leads to un wanted oxidation (absent specialprocessing) and which can contribute to distortion; (b) they do notrequire 0.4 0.5 percent carbon to provide adequate strength uponhardening. High carbon does render such prior art steels austenitic atthe forging temperatures employed and does result in high strengthsteels,

but, high carbon also can contribute to die wear and distortion. Thepresent invention minimizes this and yet is capable of delivering yieldstrengths up to l50,000 psi, if desired: and (c) they do not requirecarefully controlled atmospheres during sintering and heating forforging to prevent earburization.

It perhaps should be also mentioned that conventional pre-conditionaltreatments are unnecessary as a prerequisite to obtaining a fine grain.in prior art wrought alloy steel processing it is common, for exam ple,to hot work a steel while cooling down to and into a duplex region. Itis the pre-conditioning working operation which is largely responsiblefor a fine grain; otherwise, a coarse grain results. Forging ascontemplated herein involves virtually an isothermal operation duringwhich continuous recrystallization takes place. This contributes tomaintaining a fine grain structure but without need of preconditioning.

With regard to the roles of the individual constituents of the steels ofspecific composition given herein, nickel contributes to strength,hardenability and broadens the temperature range over which stableferriteaustenite structures can be obtained. But, an excess isunwarranted due to cost and may increase resistance to flow at 1400F. to1500F. by unnecessarily increasing the amount of austenite. Moreover,nickel is particularly useful in bringing about the propermicrostructure particularly in counterbalancing the significant effectof silicon in contributing to the formation of ferrite. While manganesemight be used in lieu of nickel, toughness suffers and manganese tendsto give an oxi dation problem. It should be held to less than 0.4percent.

The molybdenum need not exceed 1.2 percent. At nickel percentages of land 3 percent the higher molybdenum levels appear to detract fromtensile strength. A range of 0.2 to 0.6 percent is satisfactory.Columbium tends to increase flow stress and preferably should not exceedabout 0.l percent. It does contribute to tensile strength and a range of0.02 to 0.08 percent is of benefit. Silicon, as noted, promotes theformation of ferrite but does lower toughness at the higher levels. Itis to advantage that it not exceed 2 percent. As to carbon, while it canbe omitted it does confer strength ening qualities and it is preferredthat at least 0.02 to 0.04 percent be present. High levels, e.g., 0.4 or0.5 percent, are unnecessary and although they could be used in aproperly balanced structure, at desired forging temperatures couldresult in virtually completely austenitic steels such that, otherfactors remaining equal, excessive die wear or distortion could ensue.Copper provides age hardening and strength.

Other elements such as chromium, aluminum, vanadium, titanium, tungstenand cobalt can be present. These constituents need not exceed 2 or 3percent each, with the aluminum plus titanium preferably not exceeding05 percent. If employed, attention must be given to their respectiveferrite, austenite forming tendencies. Aluminum and tungsten might beused in lieu of or together with lower levels of silicon for the purposeof forming ferrite. However, silicon is much preferred since tungsten isof high density and is expensive and an equivalent percentage ofaluminum would tend to impart an oxidation problem.

Where a combination of low flow stress over the temperature range ofabout l400F. 1500F coupled with a room temperature yield strength of80,000

120,000 psi and good tensile ductility (above 7.5 percent) is desired,the following range of composition is considered most advantageous:about 0.05 0.15 percent carbon, about 0.8 to 1.5 percent silicon, about0.5 to 1.2 percent nickel, about 0.2 to 0.4 percent molybdenum, about 1to 2 percent copper, up to 0.1 percent columbium and the balance iron.While this composition could be carburized, the usefulness of copper,which imparts age hardening capability, would be largely lost since anaging treatment at 900 l000F. could not be used to advantage on a highcarbon martensitic part. Thus, for carburizing, these steels should becopper-free or contain less than about 0.5 percent. For higher yieldstrengths, e.g., l30,000 psi and above, the silicon, nickel andmolybdenum levels should be about 2 to 2.5 percent, 2 to 3 percent and0.8 to 1.2 percent, respectively.

While the steels of specific composition described herein have beendirected to powder metallurgy forging, they are also useful in theproduction of wrought and cast products such as rod, plate and sheet(mill products) particularly when characterized by a finegrainedmicrostrueture.

While the present invention is useful in the production of a variety offorged products it is deemed particularly applicable in forming suchcomponents as pinions, connecting rods, gears and side gear blanks.

Although as a practical matter it is unlikely, other phases in additionto ferrite and austenite can be present at the forging temperature inamounts which do not have an adverse affect. Inclusions, e.g., sulphideand silicate inclusions, are not deemed to be phases as con templatedherein but can be present in small quantities. Upon cooling fromforging, the microstructures are comprised of ferrite and transformedproducts of austenite, e.g., martensite, bainite, etc. This will dependon composition and rate of cooling as will be appreciated by theartisan. Also, a small percentage of austenite, say, up to 5 percent,might also be present.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention as those skilled in the art will readily understand. For example, in addition to powder forging, the alloy powderscan be extruded or otherwise worked. Such modifications and variationsare considered to be within the purview and scope of the invention andappended claims.

I claim:

1. in the process of steel powder metallurgy hot forging, theimprovement of obtaining a lower flow stress during forging whichcomprises hot forging low alloy steel powder at a temperature in whichthe steel powder is characterized by a microstructure consistingessentially of ferrite and austenite, each of these phases being presentin a volume percentage of at least 4% and such that the grains of eachmutually coact to retard grain growth of the other duringrecrystallization.

2. A process in accordance with claim 1 in which the ferrite andaustenite are both present in a volume percentage of at least l percentand their respective grain sizes are at least ASTM l0.

3. A process in accordance with claim 1 in which the ferrite andaustenite are both present in a volume percentage of at least about 20percent and their respective grain sizes are ASTM 12 or finer.

4. A process in accordance with claim I in which the ferrite is at least60 percent by volume.

5. A process in accordance with claim 1 in which the alloy steel powderforged is of a composition consisting of about 0.05 to 0.15 percentcarbon, about 0.8 to 2.5 percent silicon, up to 2 percent manganese,about 0.5 to 4 percent nickel, about 0.2 to 2 percent molybdenum, up toabout 0.2 percent columbium, up to 2 percent copper, about 0.01 to 0.25percent oxygen, the balance being essentially iron, the particlesforming the powder being of irregular shape and further characterized bya particle size of not greater than about 500 microns, a grain size notless than an average ASTM grain size of about 10 and with their outersurfaces being substantially enveloped by an oxide film not greater thanabout l0 microns in thickness.

6. A process in accordance with claim 5 in which the oxygen contents ofthe alloy steel does not exceed about 0.15 percent, the particle size isless than 275 microns and the oxide film is not greater than about 5microns.

7. A process in accordance with claim 5 in which the alloy compositioncontains copper in an amount sufficient to impart significant hardeningand strength upon being cooled from an aging treatment of 900F.- l 000F.

8. A process in accordance with claim 5 in which the alloy contains atleast 1 percent copper, at least 0.0l percent columbium and in which themolybdenum does not exceed 1.2 percent.

9. A process in accordance with claim 1 in which the alloy steelcontains from 0.8 to L5 percent silicon, up to 1 percent manganese,about 0.5 to 1.2 percent nickel and about 0.2 to 0.5 percent molybdenum.

10. A process in accordance with claim 9 in which the alloy steelcontains from about 1 to 2 percent copper.

1]. A process in accordance with claim 1 in which the alloy steelcontains from 2 to 2.5 percent silicon, about 2 to 3 percent nickel,about 0.8 to 1.2 percent molybdenum and about 1 to 2 percent copper.

12. A process in accordance with claim 1 in which the alloy steelcontains up to 0.4 percent carbon, about 0.8 to 2.5 percent silicon, upto 2 percent manganese, about 0.5 to 4 percent nickel, about 0.2 to 2percent molybdenum, up to 0.2 percent columbium, up to 2 percent copper,oxygen present in an amount not greater than 1, up to 3 percent each ofcobalt, chromium, tungsten, vanadium, up to 0.5 percent in total ofaluminum plus titanium and the balance essentially iron.

13. A process in accordance with claim 2 in which the alloy steel powderforged is of a composition consisting of about 0.05 to 0. l5 percentcarbon, about 0.8 to 2.5 percent silicon, up to 2 percent manganese,about 0.5 to 4 percent nickel, about 0.2 to 2 percent molybdenum, up toabout 0.2 percent columbium, up to 2 percent copper, about 0.01 to 0.25percent oxygen, the balance being essentially iron, the particlesforming the powder being of irregular shape and further characterized bya particle size of not greater than about 500 microns, a grain size notless than an average ASTM grain size of about 10 and with their outersurfaces bcing substantially enveloped by an oxide film not greater thanabout 10 microns in thickness.

14. A process in accordance with claim 2 in which the alloy steel powdercontains up to 0.4 percent carbon, about 08 to 2.5 percent silicon, upto 2 percent manganese, about 0.5 to 4 percent nickel, about 0.2 to 2percent molybdenum, up to 0.2 percent columbium, up to 2 percent copper,oxygen present in an amount not greater than 1 percent, up to 3 percenteach of cobalt, chromium, tungsten, vanadium, up to 05 percent in totalof aluminum plus titanium and the balance essentially iron.

1. IN THE PROCESS OF STEEL POWDER MELTALLURGY HOT FORGING, THEIMPROVEMENT OF OBTAINING A LOWER FLOW STRESS DURING FORGING WHICHCOMPRISES HOT FORGING LOW ALLOY STEEL POWDER AT A TEMPERATURE IN WHICHTHE STEEL POWDER IS CHARACTERIZED BY A MICROSTRUCTURE CONSISTINGESSENTIALLY OF FERRITE AND AUSTENITE, EACH OF THESE PHASES BEING PRESENTIN A VOLUME PERCENTAGE OF
 2. A process in accordance with claim 1 inwhich the ferrite and austenite are both present in a volume percentageof at least 10 percent and their respective grain sizes are at leastASTM
 10. 3. A process in accordance with claim 1 in which the ferriteand austenite are both present in a volume percentage of at least about20 percent and their respective grain sizes are ASTM 12 or finer.
 4. Aprocess in accordance with claim 1 in which the ferrite is at least 60percent by volume.
 5. A process in accordance with claim 1 in which thealloy steel powder forged is of a composition consisting of about 0.05to 0.15 percent carbon, about 0.8 to 2.5 percent silicon, up to 2percent manganese, about 0.5 to 4 percent nickel, about 0.2 to 2 percentmolybdenum, up to about 0.2 percent columbium, up to 2 percent copper,about 0.01 to 0.25 percent oxygen, the balance being essentially iron,the particles forming the powder being of irregular shape and furthercharacterized by a particle size of not greater than about 500 microns,a grain size not less than an average ASTM grain size of about 10 andwith their outer surfaces being substantially enveloped by an oxide filmnot greater than about 10 microns in thickness.
 6. A process inaccordance with claim 5 in which the oxygen contents of the alloy steeldoes not exceed about 0.15 percent, the particle size is less than 275microns and the oxide film is not greater than about 5 microns.
 7. Aprocess in accordance with claim 5 in which the alloy compositioncontains copper in an amount sufficient to impart significant hardeningand strength upon being cooled from an aging treatment of 900*F.-1000*F.8. A process in accordance with claim 5 in which the alloy contains atleast 1 percent copper, at least 0.01 percent columbium and in which themolybdenum does not exceed 1.2 percent.
 9. A process in accordance withclaim 1 in which the alloy steel contains from 0.8 to 1.5 percentsilicon, up to 1 percent manganese, about 0.5 to 1.2 percent nickel andabout 0.2 to 0.5 percent molybdenum.
 10. A process in accordance withclaim 9 in which the alloy steel contains from about 1 to 2 percentcopper.
 11. A process in accordance with claim 1 in which the alloysteel contains from 2 to 2.5 percent silicon, about 2 to 3 percentnickel, about 0.8 to 1.2 percent molybdenum and about 1 to 2 percentcopper.
 12. A process in accordance with claim 1 in which the alloysteel contains up to 0.4 percent carbon, about 0.8 to 2.5 percentsilicon, up to 2 percent manganese, about 0.5 to 4 percent nickel, about0.2 to 2 percent molybdenum, up to 0.2 percent columbium, up to 2percent copper, oxygen present in an amount not greater than 1, up to 3percent each of cobalt, chromium, tungsten, vanadium, up to 0.5 percentin total of aluminum plus titanium and the balance essentially iron. 13.A process in accordance with claim 2 in which the alloy steel powderforged is of a composition consisting of about 0.05 to 0.15 percentcarbon, about 0.8 to 2.5 percent silicon, up to 2 percent manganese,about 0.5 to 4 percent nickel, about 0.2 to 2 percent molybdenum, up toabout 0.2 percent columbium, up to 2 percent copper, about 0.01 to 0.25percent oxygen, the balance being essentially iron, the particlesforming the powder being of irregular shape and further characterized bya particle size of not greater than about 500 microns, a grain size notless than an average ASTM grain size of about 10 and with their outersurfaces being substantially enveloped by an oxide film not greater thanabout 10 microns in thickness.
 14. A process in accordance with claim 2in which the alloy steel powder contains up to 0.4 percent carbon, about0.8 to 2.5 percent silicon, up to 2 percent manganese, about 0.5 to 4percent nickel, about 0.2 to 2 percent molybdenum, up to 0.2 percentcolumbium, up to 2 percent copper, oxygen present in an amount notgreater than 1, up to 3 percent each of cobalt, chromium, tungsten,vanadium, up to 0.5 percent in total of aluminum plus and the balanceessentially iron.
 15. A process in accordance with claim 3 in which thealloy steel powder contains up to 0.4 percent carbon, about 0.8 to 2.5percent silicon, up to 2 percent manganese, about 0.5 to 4 percentnickel, about 0.2 to 2 percent molybdenum, up to 0.2 percent columbium,up to 2 percent copper, oxygen present in an amount not greater than 1percent, up to 3 percent each of cobalt, chromium, tungsten, vanadium,up to 0.5 percent in total of aluminum plus titanium and the balanceessentially iron.